Code Examples

8-bit pixel formats are the easiest to understand. Since it is an 8-bit format, we have 8 BitsPerPixel and 1 BytesPerPixel. Since BytesPerPixel is 1, all pixels are represented by a Uint8 which contains an index into palette->colors. So, to determine the color of a pixel in an 8-bit surface: we read the color index from surface->pixels and we use that index to read the SDL_Color structure from surface->format->palette->colors. Like so:

Pixel formats above 8-bit are an entirely different experience. They are considered to be "TrueColor" formats and the color information is stored in the pixels themselves, not in a palette. The mask, shift and loss fields tell us how the color information is encoded. The mask fields allow us to isolate each color component, the shift fields tell us the number of bits to the right of each component in the pixel value and the loss fields tell us the number of bits lost from each component when packing 8-bit color component in a pixel.

/* Extracting color components from a 32-bit color value */SDL_PixelFormat*fmt;SDL_Surface*surface;Uint32temp,pixel;Uint8red,green,blue,alpha;...fmt=surface->format;SDL_LockSurface(surface);pixel=*((Uint32*)surface->pixels);SDL_UnlockSurface(surface);/* Get Red component */temp=pixel&fmt->Rmask;/* Isolate red component */temp=temp>>fmt->Rshift;/* Shift it down to 8-bit */temp=temp<<fmt->Rloss;/* Expand to a full 8-bit number */red=(Uint8)temp;/* Get Green component */temp=pixel&fmt->Gmask;/* Isolate green component */temp=temp>>fmt->Gshift;/* Shift it down to 8-bit */temp=temp<<fmt->Gloss;/* Expand to a full 8-bit number */green=(Uint8)temp;/* Get Blue component */temp=pixel&fmt->Bmask;/* Isolate blue component */temp=temp>>fmt->Bshift;/* Shift it down to 8-bit */temp=temp<<fmt->Bloss;/* Expand to a full 8-bit number */blue=(Uint8)temp;/* Get Alpha component */temp=pixel&fmt->Amask;/* Isolate alpha component */temp=temp>>fmt->Ashift;/* Shift it down to 8-bit */temp=temp<<fmt->Aloss;/* Expand to a full 8-bit number */alpha=(Uint8)temp;printf("Pixel Color -> R: %d, G: %d, B: %d, A: %d\n",red,green,blue,alpha);...

Remarks

Everything in the pixel format structure is read-only.

A pixel format has either a palette or masks. If a palette is used Rmask, Gmask, Bmask, and Amask will be 0.